Compositions and methods for drying patterned wafers during manufacture of integrated circuitry products

ABSTRACT

Drying of patterned wafers is achieved in a manner effecting removal of water from the patterned wafers without collapse or deterioration of the pattern structures thereof. The drying is carried out in one aspect of the invention with a composition containing supercritical fluid, and at least one water-reactive agent that chemically reacts with water to form reaction product(s) more soluble in the supercritical fluid than water. Various methodologies are described for use of supercritical fluids to dry patterned wafers, which avoid the (low water solubility) deficiency of supercritical fluids such as supercritical CO 2 .

BACKGROUND

The present invention relates to compositions and methodology for dryingpatterned wafers during the manufacture of integrated circuitryproducts.

BACKGROUND OF THE RELATED ART

During the manufacture of integrated circuit (IC) products, residualliquids such as water, alcohols, and the like must be completely removedfrom patterned wafers by drying operations. However, when criticaldimensions are smaller than about 100 nanometers (nm), it is difficultto remove residual water from the patterned wafers with high aspectratio trenches and vias without causing collapse of the lithographicpattern features.

For example, in the development of photo-exposed lithographic resists,patterned images are often dried with hexanes and nitrogen, or withisopropanol and nitrogen. These conventional drying methods do not workwell for images having a critical dimension width <100 nm and aspectratio greater than 1. At such feature dimensions, the surface tension ofisopropanol or hexane pulls the images together, leading to collapse ofthe lithographic resist and loss of the patterned image, or todegradation of the polymeric resist.

The art therefore is in need of improved techniques for drying ofpatterned wafers which effect complete removal of water, alcohols, etc.,without causing collapse of the pattern features or other adverseeffects on the patterned wafers.

SUMMARY OF THE INVENTION

The present invention relates to compositions and methodology for dryingof patterned wafers to remove water, alcohols, etc. from the wafer,without causing collapse of the pattern or other adverse effect on thewafer article.

In one aspect, the present invention relates to a composition for dryinga patterned wafer to remove water therefrom, such composition comprisingsupercritical fluid, and at least one water-reactive agent thatchemically reacts with water to form reaction product(s) more soluble inthe supercritical fluid than water.

In a further aspect, the invention relates to a method of drying apatterned wafer to remove water therefrom, such method comprisingcontacting said patterned wafer with a composition comprisingsupercritical fluid, and at least one water-reactive agent thatchemically reacts with water to form reaction product(s) more soluble inthe supercritical fluid than water.

A still further aspect of the invention relates to a method of drying apatterned wafer to remove water therefrom, such method comprisingcontacting the patterned wafer with a first composition comprisingliquid CO₂, and thereafter contacting the patterned substrate with asecond composition comprising SCCO2, thereby effecting drying of thepatterned substrate without damage to the pattern thereof.

Yet another aspect of the invention relates to a method of drying apatterned wafer to remove water therefrom, such method comprising (a)contacting the patterned wafer with a first composition comprisingalcohol at pressure above about 1000 psi and temperature below 32° C.,(b) contacting the patterned wafer with a second composition comprisingan alcohol/CO₂ solution, and (c) contacting the patterned substrate witha third composition comprising SCCO2, thereby effecting drying of thepatterned substrate without damage to the pattern thereof.

Other aspects, features and embodiments of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscope (SEM) photograph of a patternedwafer showing the details of the pattern structure, utilized as acontrol sample, relative to FIGS. 2-4.

FIG. 2 is an SEM photograph of a patterned wafer of the type shown inFIG. 1, after air-drying of the wafer.

FIG. 3 is an SEM photograph of a patterned wafer of the type shown inFIG. 1, after drying of the wafer with liquid CO₂.

FIG. 4 is an SEM photograph of a patterned wafer of the type shown inFIG. 1, after drying of the wafer, first with liquid CO₂ and then withsupercritical CO₂.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

The present invention is based on the use of supercritical fluid (SCF)as a cleaning medium for drying of patterned wafers, in variousapproaches that avoid the problems incident to the use of supercriticalfluids per se.

While supercritical fluids might on first consideration be regarded aspotentially useful media for drying of patterned wafers, sincesupercritical fluids have high diffusivity, low viscosity, near-zerosurface tension, and superior penetrating ability, supercritical fluidssuch as supercritical CO₂ (SCCO2) are non-polar and therefore are notuseful for drying of patterned wafers. For example, the solubility ofwater in supercritical CO₂ is <0.1% by weight, making supercritical CO₂unsuitable for removing residual water on the patterned wafer.

The present invention overcomes the problems incident to the use ofsupercritical fluids as drying media.

While the invention is hereinafter described with specific reference toCO₂ as an illustrative supercritical fluid species, it will berecognized that the utility of the invention is not thus limited, andthat the supercritical fluid in the practice of the present inventioncan be of any suitable type. Supercritical fluids are formed underconditions at which the density of the liquid phase equals the densityof the gaseous phase of the substance. For example, carbon dioxide(CO₂), which is a gas at standard temperature and pressure, undergoes atransition from liquid to SCF above a critical point, corresponding toT_(e)≧31.1° C. and P_(e)≧72.8 atm. Once formed, the density of the SCFcan be varied from liquid-like to gaseous-like, yielding differentsolvation abilities, by varying the pressure and temperature.Supercritical fluids have a density/solubility and diffusibilityapproaching that of the liquid and gaseous phase, respectively.Additionally, the surface tension of SCFs is negligible.

Because of its readily manufactured character, lack of toxicity andnegligible environmental effects, supercritical CO₂ is a preferred SCFin the broad practice of the present invention, although the inventionmay be practiced with any suitable SCF species, with the choice of aparticular SCF depending on the specific application involved. Otherpreferred SCF species useful in the practice of the invention includeoxygen, argon, krypton, xenon, and ammonia.

In a first embodiment, supercritical fluids are used as drying media forpatterned wafers in drying compositions that include one or morewater-reactive agents that chemically react with water on the patternedwafer to form reaction product species that are more soluble in thesupercritical fluid than water.

As an illustrative example, hexafluoroacetone (HFA) is usefully employedas a water-reactive agent in SCCO2 to provide a highly effectivesupercritical fluid composition for drying of patterned wafers. In suchcomposition, HFA reacts instantly with water and quantitatively forms asoluble and volatile diol as depicted in the following reaction:H₂O+CF₃ COCF₃→CH₃C(OH)₂CF₃

The product diol, CH₃C(OH)₂CF₃, is highly soluble in SCCO2 and isreadily dissolved by the supercritical fluid, thereby effectivelyremoving water from the patterned wafer substrate with which thesupercritical fluid composition, comprising SCCO2 and HFA, is contacted.

More generally, the water-reactive agent in the supercriticalfluid-based wafer drying composition can be of any suitable type,including for example, other halogenated aldehydes and ketones;halogenated diketones, e.g., 1,1,1,5,5,5-hexafluoro-2,4-pentanedione,alternatively denoted as (hfac)H; halogenated esters; carboxylicanhydrides, e.g., (CH₃CO)₂O; siloxanes, halogenated silanes; and anyother compounds and materials that easily react with water and formderivatives soluble in supercritical CO₂ or other supercritical fluidspecies.

Generally, the water-reactive agent can be formulated in thesupercritical fluid composition at any suitable concentration that iseffective for water removal from the patterned wafer substrate. Invarious embodiments, depending on the particular supercritical fluidspecies employed, the concentration of the water-reactive agent can be aconcentration in a range of from about 0.01 to about 10.0% by weight,based on the total weight of the supercritical fluid and thewater-reactive agent, with concentrations of from about 0.1 to about7.5% by weight, on the same total weight basis being more preferred, andfrom about 0.1 to about 5.0% by weight, on the same total weight basisbeing most preferred.

The supercritical fluid drying composition in addition to thesupercritical fluid and the water-reactive agent, can contain othercomponents, e.g., co-solvent(s) for removal of components other thanwater from the patterned substrate, active agent(s) other than thewater-reactive agent, surfactant(s), chelating agent(s), etc., asnecessary or desirable in a given application of the drying composition.

As used in such context, an “active agent” is a material that induceschemical reaction and/or physical enhancement of solubility, either inthe cleaning composition, or at the surface of the patterned substratestructure, to enhance the cleaning and/or removal action of thecomposition, relative to a corresponding composition lacking suchmaterial.

Illustrative co-solvent species can include, but are not limited to,xylene, methanol, ethanol, and higher alcohols, N-alkylpyrrolidiones,such as N-methyl-, N-octyl-, or N-phenyl-pyrrolidones,dimethylsulfoxide, sulfolane, catechol, ethyl lactate, acetone, methylethyl ketone, butyl carbitol, monoethanolamine, butyrol lactone,diglycol amine, alkyl ammonium fluoride 1-butyrolactone butylenecarbonate, ethylene carbonate, propylene carbonate, etc.

The co-solvent species may be a single component co-solvent or two ormore solvent components. The co-solvent may be present in thesupercritical fluid-based drying composition at any suitableconcentration, consistent with solubility of the co-solvent in thesupercritical fluid.

Examples of active agents include, without limitation, acids, bases,reducing agents, and oxidizing agents. When a reducing agent issolubilized in the supercritical fluid, the reducing agent may requireactivation, e.g., by an activation process involving thermal, optical,and/or sonic activation.

Surfactants useful in the drying compositions of the present inventionmay likewise be of any suitable type, including anionic, neutralcationic, and zwitterionic types. Illustrative surfactant speciesinclude, without limitation, acetylenic alcohols and diols, and longalkyl chain secondary and tertiary amines.

Chelating agents useful in the drying compositions of the invention maybe of any suitable type including, for example, polycarboxylic acidssuch as iminodiacetic acid and lauryl ethylenediamine triacetic acid,β-diketones such as: 2,4-pentanedione; 1,1,1-trifluoro-2,4-pentandione;and 1,1,1,5,5,5-hexafluoro-2,4-pentanedion, substituteddithiocharbanates, malonic acid esters, and polyethylene glycols.

Illustrative species of acids useful in drying compositions of theinvention include, without limitation, perfluorocarboxyic acids, andalkyl or aryl sulfonic acids. Illustrative species of bases useful indrying compositions of the invention include, but are not limited to,amines, such as alkyl amines. Oxidizing agents useful in the broadpractice of the invention include, without limitation, oxygen, ozone andnitrous oxide. Reducing agents usefully employed in the dryingcompositions of the invention include, without limitation, hydrogen,ammonia, xylenes, hydrides, silane, alkylsilanes, hydrazine hydrate oralkyl hydrazine.

Various compositions can be employed within the scope of the presentinvention, and such compositions can alternatively comprise, consist orconsist essentially of specific identified component(s) describedherein, as desired in a given application of the invention.

The contacting of the patterned substrate with the drying composition iscarried out for a suitable period of time, which in a specificembodiment can for example be on the order of from about 20 to about 60seconds, although other (longer or shorter) periods of contacting may beusefully employed depending on the nature and amount of the water to beremoved from the patterned substrate, and the process conditionsemployed for drying.

Following drying of the patterned substrate, the contacting vessel inwhich the supercritical fluid-based composition is contacted with thepatterned substrate can be rapidly decompressed to separate thesupercritical fluid composition from the patterned substrate and exhaustthe regasified supercritical fluid from the contacting vessel, so thatthe non-supercritical component(s), such as the soluble water reactionproduct(s), can be entrained in the regasified supercritical fluid andlikewise be removed from the drying locus.

Such decompression step may be conducted for a suitable period of time,e.g., on the order of 10-40 seconds, although longer or shorter timesmay be desirable depending on the character of the material to beremoved from the patterned substrate and the specifics of the process.If necessary, repeated cycles of contacting and decompression may beutilized, to achieve substantially complete removal of the water fromthe patterned substrate article.

The above-described composition and method can be usefully employed toclean residual water from small dimensions on semiconductor substratessubsequent to photolithographic image patterning processes without theoccurrence of pattern collapse.

In another aspect, the present invention contemplates use ofsupercritical fluid-based drying compositions as part of a two-stepprocess for obtaining efficient drying without the collapse of thepattern features. In this drying process, an initial drying step iscarried out by contacting the patterned substrate with liquid CO₂,followed by a second drying step including contacting the patternedsubstrate with SCCO2, to achieve drying of the patterned substratewithout accompanying damage to the patterned wafer.

In this two-step drying process, the liquid phase CO₂ in the first stephas a higher density than SCCO2, so that it can solvate water and/oralcohol on the patterned substrate, but such contacting alone is notsufficient to complete the drying of the patterned substrate, andtherefore the second step of rinsing the patterned substrate is employedto effect complete removal of the water and/or alcohol on the substrate.

The advantages of the two-step drying process described above weredemonstrated using patterned wafers of the type shown in FIG. 1

FIG. 1 is a scanning electron microscope (SEM) photograph of a patternedwafer showing the details of the pattern structure, utilized as acontrol sample, relative to FIGS. 2-4.

In the drying tests, the test wafers were immersed in water and then inpure alcohol for several minutes each, and the wafers were then placedin the cleaning chamber for drying.

A first test wafer was air-dried. FIG. 2 is an SEM photograph of apatterned wafer of the type shown in FIG. 1, after such air-drying ofthe wafer. As shown in FIG. 2, the water and alcohol were not completelyremoved, and the residual amounts of these contaminants causedcollapsing of the pattern structure to occur.

A second test wafer was dried with liquid CO₂. FIG. 3 is an SEMphotograph of a patterned wafer of the type shown in FIG. 1, after suchdrying of the wafer with liquid CO₂. As shown in FIG. 3, the water andalcohol were not completely removed, and the residual amounts of thesecontaminants caused a high level of collapse of the pattern structure totake place.

A third test wafer was dried in a two-step process as describedhereinabove, including a first step of contacting the patterned waferwith liquid CO₂ and a second step of contacting the patterned wafer,after the first contacting step, with supercritical CO₂. FIG. 4 is anSEM photograph of a patterned wafer of the type shown in FIG. 1, aftersuch drying of the wafer, first with liquid CO₂ and then withsupercritical CO₂. The pattern structure of the wafer was not altered bythis two-step drying operation, and the pattern was retained in a mannerconsistent with the control wafer (compare FIGS. 1 and 4).

The two-step process described above can be carried out at any suitableprocess conditions and for any suitable durations in the respectivefirst and second steps. In one embodiment, the first liquid CO₂contacting step can be carried out at temperature in a range of fromabout 20° C. to about 30° C. for a time in a range of from about 0.5 toabout 20 minutes, and the second SCCO2 contacting step can be carriedout at temperature in a range of from about 32° C. to about 75° C. for aduration in a range of from about 0.5 to about 20 minutes.

In yet another aspect, the present invention contemplates use ofsupercritical fluid-based drying compositions as part of a three-stepprocess for obtaining efficient drying without the collapse of thepattern features.

In this drying process, an initial drying step is carried out in whichthe patterned substrate is contacted with alcohol at a pressure aboveabout 1000 psi and temperature below the critical temperature of CO₂,32° C., for a suitable period of time, e.g. from about 1 minute to about15 minutes. The alcohol can be a single component alcohol, or it can bea mixture of alcohol species, and the alcohol can be recirculated incontact with the patterned substrate, or it can be contacted in a batchor a semibatch mode.

The second step is carried out after the alcohol contacting step, andinvolves contacting the patterned substrate with an alcohol/CO₂ solutionto remove alcohol from the first contacting step. This second steppreferably is carried out with recirculation of the alcohol/CO₂ solutionthrough the contacting chamber containing the patterned substrate,although the contacting may be carried out in a single-pass manner, orin a batch or semi-batch mode of operation. The second step contactingcan be carried out at a temperature in a range of from about 22° C. toabout 31° C. for a duration in a range of from about 0.5 to about 20minutes. As in the first step, the alcohol can be a single componentalcohol, or it can be a mixture of alcohol species.

The alcohol utilized in the first and second contacting steps can be thesame as or different from each other. The alcohol can be of any suitabletype. In one embodiment of the invention, such alcohol comprises a C₁-C₄alcohol (i.e., methanol, ethanol, propanol, or butanol), or a mixture oftwo or more of such alcohol species.

The third step is carried out after the alcohol/CO₂ solution contactingstep, and involves rinsing the patterned substrate with SCCO2. Suchsupercritical fluid rinse step can be carried out at a temperature in arange of from about 32° C. to about 75° C. and pressure in a range offrom about 80 to about 300 atm., for a duration in a range of from about0.5 to about 30 minutes. Each of the first, second and third steps canbe carried out in a same process vessel, suitably valved, piped andmanifolded for delivery, and, if desired, recirculation, of thesuccessive drying compositions.

The alcohol/CO₂ solution can be formulated with the alcohol at anysuitable concentration. In one embodiment, the concentration of thealcohol in the alcohol/CO₂ solution is from about 1 to about 15% byweight, based on the total weight of the alcohol and CO₂ components inthe alcohol/CO₂ solution. The alcohol/CO₂ solution can also beformulated with other components as desired, such as those (e.g.,co-solvents, active agent(s), surfactant(s) and/or chelating agent(s))illustratively described hereinabove.

Although the invention has been described herein with reference tovarious specific aspects, features and embodiments, it will beappreciated that the invention is not thus limited, but rather extendsto and encompasses other variations, modifications and embodiments, suchas will suggest themselves to those of ordinary skill in the art, basedon the disclosure herein. Accordingly, the invention is intended to bebroadly interpreted and construed, as including all such othervariations, modifications and embodiments, within the spirit and scopeof the invention as hereinafter claimed.

1-25. (canceled)
 26. A method of drying a patterned wafer to removewater therefrom, said method comprising contacting said patterned waferwith a first composition comprising liquid CO₂, and thereaftercontacting the patterned substrate with a second composition comprisingSCCO2, thereby effecting drying of the patterned substrate withoutdamage to the pattern thereof.
 27. The method of claim 26, wherein thefirst composition contacting step is carried out at temperature in arange of from about 20 to about 30° C.
 28. The method of claim 27,wherein the first composition contacting step is carried out for a timein a range of from about 0.5 to about 20 minutes.
 29. The method ofclaim 26, wherein the second composition contacting step is carried outat temperature in a range of from about 32 to about 75° C.
 30. Themethod of claim 29, wherein the second composition contacting step iscarried out for a time in a range of from about 0.5 to about 20 minutes.31. The method of claim 26, wherein the first composition contactingstep is carried out at temperature in a range of from about 20 to about30° C. for a time in a range of from about 0.5 to about 20 minutes, andthe second composition contacting step is carried out at temperature ina range of from about 32 to about 75° C. for a time in a range of fromabout 0.5 to about 20 minutes.
 32. A method of drying a patterned waferto remove water therefrom, said method comprising (a) contacting saidpatterned wafer with a first composition comprising alcohol at pressureabove about 1000 psi and temperature below 32° C., (b) contacting saidpatterned wafer with a second composition comprising an alcohol/CO₂solution, and (c) contacting the patterned substrate with a thirdcomposition comprising SCCO2, thereby effecting drying of the patternedsubstrate without damage to the pattern thereof.
 33. The method of claim32, wherein said contacting (a) is carried out for a period of fromabout 1 minute to about 15 minutes.
 34. The method of claim 32, whereinsaid alcohol of said first composition comprises at least one C₁-C₄alcohol.
 35. The method of claim 32, wherein said alcohol of said firstcomposition comprises methanol.
 36. The method of claim 32, wherein saidalcohol of said first composition is the same as alcohol of the secondcomposition.
 37. The method of claim 32, wherein said first compositionis recirculated in contact with the patterned wafer.
 38. The method ofclaim 32, wherein the second composition is recirculated in contact withthe patterned wafer.
 39. The method of claim 32, wherein the thirdcomposition is recirculated in contact with the patterned wafer.
 40. Themethod of claim 32, wherein said contacting (b) is carried out attemperature in a range of from about 22 to about 31° C.
 41. The methodof claim 32, wherein said contacting (b) is carried out for a period offrom about 0.5 to about 20 minutes.
 42. The method of claim 32, whereinsaid contacting (c) is carried out at temperature in a range of fromabout 32 to about 75° C.
 43. The method of claim 32, wherein saidcontacting (c) is carried out for a time of from about 0.5 to about 20minutes.
 44. The method of claim 32, wherein concentration of saidalcohol in said second composition is in a range of from about 1 toabout 15% by weight, based on total weight of said alcohol and said CO₂therein.
 45. The method of claim 32, wherein the contacting steps (a),(b) and (c) are carried out in a same chamber.